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Uma Bhatt(IARC-UAF)4 April 2002

Climate• synthesis of weather in aparticular region• monthly averages• climate influences life• life sensitive to climate

• Temperature & Precipitation

What is Climate?

Main points about Climate• Uneven solar heating• Heat transported to compensate(50% atmosphere and 50% in ocean)

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Simplistic Overview of Global Climate

SUN•Heats the Earth unevenly

ATMOSPHERE•Circulation acts to redistribute heat

OCEAN•Circulation acts to redistribute heat

LAND•Influences the job of the atmosphere and ocean

CLIMATE•Complex state of affairs that result due to the above

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Temperature

• Most widely recognized variable• Global average temperature @ surface of earth 288˚K, 15˚C, or 59˚F• Coldest -128˚F in Antarctica to warmest of 136˚F in Libya

Lapse rate - temperaturevariation with height

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-62-62-46-273273531-1-24-49-58-61MIN

96444665849094968974534750MAX

All-timerecord

DECNOVOCTSEPAUGJULJUNMAYAPRMARFEBJAN# years 42

Monthly Temperature Extremes for Fairbanks

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Balance at Earth’s surface

EARTH’S SURFACE

IncomingSolar Radiation

Outgoing TerrestrialRadiation

Evaporation

Conduction

Ocean temperature function of •‘Total’ heat • heat brought by currents

Solar - Longwave radiation - Evaporation - Conduction = Tota

lossesgain

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Seasons results from 23.˚ degree tilt of earth’s axis

Sun is closest to earth in January and farthest in JulyWhat if the earth’s axis did not tilt?

Tropics get more solar radiation per area than poles.Sun is more directly overhead, spread over less area.What if the earth’s axis did not tilt?

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Amount of Solar radiation arriving at earth inversely proportional to distance squared

149,600,000 km from Sun1.49 x 1011 m (RS-E)

• Radiance at sun’s surface (Ss) is 6.3 x 107 W/m2

• Radius of sun (Rs) 7.0 x 108 m

S R S RS E s s0

2 2

− = S SR

RWms

s

S E

0

2

2

21380= ≈−

−

Solar Constant - amount of solar radiation reaching the top of the earths atmosphere

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Planetary Albedo is total amount of Solar radiation reflected by earth

• Average global albedo is 30% (0.3)function of clouds and reflectivity of surfaces

• Average solar radiation reaching surface is 241W/m2

( ) ( . )( )14

0 7 13804

2410

2

2

2−= = −A S R

RWmE

E

ππ

Area of Earth’s disk being bathed in sunlight

Total Area of Earth’s surface

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Distribution of Solar Energy in Watts per meter squared

•Net Solar 3 times greater in Tropics than at Poles

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Chemical Composition of Atmosphere

Atmospheric composition (by volume), top three gasses• 78% Nitrogen (N2)• 21% Oxygen (O2)• 1% Argon

Gasses important for absorption and emission of radiation < 1%• water vapor• CO2, carbon dioxide• Ozone

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Infrared Radiation emitted by earth some absorbed by atmosphere

0.4-7µµµµm 0.7-1.2µµµµm 7-25µµµµm

•Solar Absorption (yellow)0.4-.7 µµµµm (visible, 45% ) transparent0.7-1.2 µµµµm (near i.r., 37% )

• Atmospheric Absorption (green) 7-25 µµµµm (far i.r., 37% ) 9.6 µµµµm Ozone < 8 µµµµm Water11-15 Carbon Dioxide> 15 Water Vapor

incoming solar radiationoutgoing terrestrial radiation

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Net Radiative (Sum of incoming and outgoing) Heat in July

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Net Radiative Heat in January

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Global Wind pattern

Easterlies

Westerlies(from west)

Easterlies(from east)

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Global Wind pattern

Easterlies

Westerlies(from west)

Easterlies(from east)

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Surface Pressure and Wind Patterns

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Northern Hemispheric Jet Stream: River of Air

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Average Surface Circulation of World Ocean

• Ocean drift currents - wind generated motion• Eastward (westward) currents in westerly (easterly) wind regions• North equatorial counter current, exception

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Air versus Sea Water and Land

Air Water Land -inorg (org)Density kg/m3 1.275 1000 2600(1300) at 0˚C

Specific Heat 1004 4182 733 (1921)cp (liquid water) at 0˚C, J/kg˚C

• Oceans temperatures change slower than air (or land)• Solar radiation absorbed into greater depth of ocean than land ==> faster cooling/warming of land than ocean

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Topographic Impacts on Climate are Important

•Northern Hemisphere versus Southern Hemisphere•Coastal Climates - temperate•Continental Climates - hot summers and cold winters•Midwestern US Storms•Mountains

Alps - southern Europe warmHimalayas - monsoon circulation

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Global Climate Map Influenced by latitude & topography

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ENSO since 1950

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1997-98 El Niño Declared Warmest Ever

http://topex-www.jpl.nasa.gov/enso97/el_nino_1997.htmld

• Historical Background• 3-7 years irregular• Tied to Seasonal cycle

WHITE= sea level 5 - 12 in. above normalwater warmer than normal by up to 10 degrees F

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Cold, Neutral, and Warm Equatorial Pacific SSTs

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North Atlantic Oscillation

Negative Phase Positive Phase• Positive Phase Stronger pressure gradien More storms• Negative Phase Weaker pressure gradient Fewer storms

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Volcanic Eruptions act to Cool Climate

Composite global surface temperature change near the timeof the five volcanos producing the greatest optical depthssince 1880: Krakatau (1883), Santa Maria (1902), Agung(1963), El Chichon (1982) and Pinatubo (1991).

•The main gas emitted by the volcanos, sulfurdioxide, over a period of weeks combines withoxygen and water to form sulfuric acid gas.• This gas then condenses into fine droplets or"aerosols” that form a haze, similar to the haze• Volcanic haze scatters some of the incomingsunlight back to space, thus reducing solar heating ofthe Earth'ssurface.

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Summary

• Climate•Uneven Solar Heating between Equator and Poles

• Heat Balance of the Climate• ‘Greenhouse’ effect operates naturally

• Heat Transport for Balance• Ocean and Atmosphere are important for balance

• Examples of Natural Climate Variability• El Niño• North Atlantic Oscillation• Volcanic Eruptions

• What next?• Anthropogenic Increase of Greenhouse Gases• Evidence for Change• Change vs Natural Variability